Form Of Dichogamy Research Articles

A rare duodichogamous flowering system in monoecious Toona sinensis (Meliaceae)

BackgroundDuodichogamy is the rarest form of dichogamy in angiosperms, which is characterized by flowering in the sequence of male→female→male. Disentangling factors promoting duodichogamy require the discovery of more duodichogamous species in angiosperms. However, extremely limited information on duodichogamous species makes it difficult to make general conclusions. Given the inflorescence morphology and flowering characteristics, the Meliaceae family is highly likely to contain duodichogamous species.MethodsWe selected 48 individuals from 20 populations in Korea and investigated their flower morphology, arrangement of flowers by sexual condition within inflorescences, and flowering phases and duration of male and female flowers of Toona sinensis (Meliaceae) for 5 years (2011–2015) to determine if the species shows duodichogamous flowering.ResultsToona sinensis belonging to Meliaceae possessed functionally unisexual flowers with rudimentary parts of the opposite sex. The floral organs in male were larger than those in female, except for ovary length and width. In dichasium, male flowers were observed on primary or lateral branches, whereas female flowers were borne only on lateral branches. Overall, individuals from six different populations flowered in the male→female→male sequence, thereby male is blooming far longer than female flowers at the level of individual trees (male vs. female = 17–20 days vs. 2–4 days).ConclusionsThis is the first study to report a duodichogamously flowering species, T. sinensis, within Meliaceae. Several flowering characteristics observed from T. sinensis may be important clues used to discover additional duodichogamous Meliaceae species. Short flowering period and relatively small number of female flowers, which is analogous to reduced ovule numbers observed in other duodichogamous species, may intensify male–male competition in T. sinensis. This study contributed to narrowing down potential candidates of duodichogamy based on their geographic distributions and flowering time.

Floral ecology of Oreocharis acaulis (Gesneriaceae): An exceptional case of “preanthetic” protogyny combined with approach herkogamy

Protogyny is supposed to represent the ancestral form of dichogamy in the angiosperms, but is rare in advanced groups such as the Asteridae, in which protandry prevails by far. Here we report on an unusual form of protogyny combined with herkogamy in a Chinese species of Gesneriaceae (Asteridae–Lamiales): Oreocharis acaulis (formerly Opithandra acaulis). This is characterized by a conspicuous protrusion of the style from the flower bud and the stigma becoming receptive before corolla opening (female-only stage; preanthetic protogyny) and both sexes staying functional during anthesis (hermaphroditic stage), with the stigma presented above the anther level (approach herkogamy). The plants studied were found to be self-compatible, but autonomous self-pollination and apomixis were not observed. Successful pollination was found to depend fully on the presence of insect pollinators (Bombus sp.). The visiting frequency was higher in the hermaphroditic stage (in which also more nectar was produced) than in the female-only stage. The out-crossed flower buds opened earlier and had a shorter flowering period than selfed flowers. Similarly, the outcross-pollen germinated earlier and the pollen tube growth was faster than in self-pollen. Anthers, pistil and corolla of O. acaulis obviously form an integrative functional unit in which the elongated style plays a key role both in pollen-dispensing and pollen-deposition. The combination of preanthetic protogyny with herkogamy has probably arisen through selection for promoting out-crossing and prolonging the exposition time of the receptive stigma in order to capture a higher amount of pollen grains. This may be understood as a strategy to cope with scarcity of pollinators in the plants’ habitat.

Michauxia (Campanulaceae): A Western Asian Genus Honoring a North American Pioneer Botanist

Abstract Michauxia honors Andre Michaux. It is a genus of herbaceous plants with an eastern Mediterranean and trans-Caucasian distribution. This paper is a brief introduction to the genus emphasizing its most spectacular member, M. campanuloides, which exhibits a distinctive form of dichogamy.

Protogyny in Apiaceae, subfamily Apioideae: systematic and geographic distributions, associated traits, and evolutionary hypotheses

Apiaceae subfamily Apioideae is characterised by intra- and interfloral dichogamy. There are two distinct patterns: multicycle protandry and multicycle protogyny. Protogyny is almost completely restricted to New World genera. We determined the form of floral dichogamy for 198 species representing 36 of the 49 genera of Apioideae native to North America north of Mexico. We also examined variation in sex expression (proportions of perfect and staminate flowers) within and among plants in populations of 16 species. The form of dichogamy was constant among congeners, with the exception of a few adichogamous selfers. The 17 protandrous genera included 11 native to both the Old and New Worlds and six endemic to the Americas. The protandrous genera were characterised by white flowers, the presence of stylopodia, decreasing proportions of staminate flowers in sequentially blooming umbels, wetter habitats, later flowering times, and eastern or transcontinental distributions. The 19 protogynous genera were all New World endemics characterised by mostly yellow or purple flowers, the absence of stylopodia, increasing proportions of staminate flowers in sequentially blooming umbels, drier habitats, earlier flowering times, and western distributions. The transition from protandry to protogyny probably occurred in the late Pliocene, coincident with adaptation to newly forming dry grassland and cold desert habitats. The evolutionary forces involved may have included selection for reproductive assurance, pollinator specialisation, or both. The distinctive patterns of within plant variation in sex expression associated with protandrous and protogynous apioids probably evolved in response to floral dichogamy.

Movement-assisted dichogamy in Atamisquea emarginata (Capparaceae)

Various aspects of the reproductive biology of Atamisquea emarginata Miers ex Hook. et Arn. were studied in a population from Tucuman, northern Argentina. Flowering took place in late (austral) spring to early summer. The creamy white, entomophilous flowers were protandrous and lasted 3.5–4.5 days. A pleasant odor along with nectar and pollen attracted 36 mostly diurnal insect species of which 41.7% were Hymenoptera, 38.9% Lepidoptera and 19.4% Diptera. However, 75% from all recorded species were infrequent, and domestic bees made ca. 94% of all visits. One halictid bee, one sphecid wasp, one myzinid wasp, four small- to medium-sized butterflies and a hawkmoth completed the set of relatively frequent insect visitors. Pollen and stigma were presented in the same place within the flower, but interference was prevented by a movement-assisted, complete dichogamy mechanism in which the bending ability of the gynophore played a fundamental role. This form of dichogamy was previously unknown in the Capparaceae. In comparison with the known species of the closely allied genus Capparis L., A. emarginata has diurnal, smaller, longer-lasting flowers, that offer much smaller nectar amounts, and that attract a rather generalized array of non-hovering visitors, while Capparis behaves as a more crepuscular-biased sphingophile or ornithophile or chiropterophile. Low levels of seed set under bagging indicates dependence on insect visits and are partly congruent with an earlier report of self-incompatibility in A. emarginata. Pollen tubes arrived to ovules in 90.6% of the inspected flowers. Fruit set of open-pollinated flowers was 43.6%–53.7%. Ninety-five percent of all ovules were regularly aborted in each fruiting ovary; thus, each fruit contained 1.2 developed seeds. Full-sized individuals were expected to produce ca. 10,700 potential offspring per year.

INCIDENCE OF MONOECY AND DICHOGAMY IN RELATION TO SELF-FERTILIZATION IN ANGIOSPERMS.

The evolution of many floral traits, including monoecy and dichogamy, has been attributed to selection for avoidance of self-fertilization. If this explanation is correct, monoecy and dichogamy should be uncommon among self-incompatible species because physiological barriers prevent self-fertilization in such species. In fact, self-fertility was independent of sexual system in a sample of 588 hermaphroditic and monoecious angiosperms. Overall, dichogamy was also equally common among self-incompatible and self-compatible species. When the different forms of dichogamy were analyzed separately, only intrafloral protogyny was associated with self-compatibility. This form of dichogamy is less common among angiosperms than intrafloral protandry, which is probably less effective at reducing self-fertilization. Thus, avoidance of self-fertilization has probably been less important in the evolution of monoecy and most forms of dichogamy than other factors, such as avoidance of pollen-pistil interference, and flexibility of resource allocation to male and female functions.

Multiple sex expressions in Cimicifuga simplex: dichogamy destabilizes hermaphroditism

Cimicifuga simplex (Ranunculaceae) has four types of individuals, differing in their sex expression: there are individuals with hermaphroditic, hermaphroditic and male (andromonoecious), only male, or only female flowers. Purely female individuals appear during the early part of the flowering period of the population, and males during the later part. Strong protandry in hermaphroditic flowers causes a shift in functional sex ratio in the population over time. This facilitates the evolution and maintenance of small proportions of unisexual individuals in the population. A hypothesis developed from this case of multiple sex expression predicts dichogamy as a near-universal feature of andro-and gynomonoecious, androdioecious, and gynodioecious species, and also specific temporal distributions for each sex form depending upon the form of dichogamy. Results of tests on large sets of species strongly support the relevance of this hypothesis.